1. Field
The following description relates to a digital frequency measuring apparatus.
2. Description of Related Art
Various frequency measuring methods are commonly used in the related art, but there may be difficulties in simultaneously providing relatively high frequency resolution as well as a relatively high sampling rate.
In detail, in terms of relatively high frequency resolution in measuring frequencies, precise control and discrimination are possible. When measuring impedance (magnitude and phase) between nodes, using a relatively high frequency resolution results in a more accurate measurement. When measuring frequency, using a relatively high sampling rate that's at least twice as fast as the highest frequency to be measured, ensures a relatively fast and accurate control.
However, as sampling rate increases, frequency resolution degrades. On the other hand, when frequency resolution is increased, the time it takes to measure the frequency increases, thereby degrading the sampling rate. The relationship of frequency resolution to sampling rate is one of the factors considered when developing frequency measuring apparatuses. As an example, frequency resolution is a value obtained by dividing the frequency of the clock signal by the sampling rate. That is, [frequency resolution=(frequency of clock signal)/(sampling rate)]. As another example, when considering the predetermined division value N, the frequency resolution is a value obtained by dividing the value (from the frequency of the clock signal times the predetermined division value N) by the sampling rate. That is, [frequency resolution=((frequency of the clock signal)*N)/(sampling rate)].
Conventional digital frequency measuring techniques measure frequency using various methods, such as an integrator using a counter. Frequency counters usually measure the number of oscillations or pulses per second in a periodic electronic signal.
The frequency measuring techniques typically use an internal oscillator having a relatively high frequency when the input frequency to be measured has a wide frequency band. However, using an oscillator with a high frequency in order to increase the resolution of the measured input frequency, decreases the sampling rate.
In conventional arts, frequency measuring techniques that use a counter is commonly used as a frequency counting method where an input frequency is measured by counting clock cycles internally-provided by a main oscillator.
In conventional frequency measuring techniques, when an input frequency is similar to or greater than that of a main oscillator, discrimination of frequencies becomes difficult.
For example, when input frequencies of 10 MHz and 9.8 MHz are counted using clock cycles of a 20 MHz main oscillator, the counter values for both cases are 2 clock cycles, making 10 MHz indistinguishable from 9.8 MHz.
As described above, in a case in which frequency measuring methods of the related art are used, satisfying both frequency resolution and sampling rate in a trade-off relationship may be problematic.
Thus, a structure for satisfying a relatively wide frequency input range is required to improve both the frequency resolution and the sampling rate.